Use a better name.

[bertos.git] / bertos / kern / preempt.c

diff --git a/bertos/kern/preempt.c b/bertos/kern/preempt.c
index f068a8a82c24d314d159e84a045422de18b55475..48a1278ebffa7b0d6df4937a417d2c08eb82b3bf 100644 (file)
--- a/bertos/kern/preempt.c
+++ b/bertos/kern/preempt.c
@@ -26,55 +26,140 @@
  * invalidate any other reasons why the executable file might be covered by
  * the GNU General Public License.
  *
- * Copyright 2001, 2004 Develer S.r.l. (http://www.develer.com/)
- * Copyright 1999, 2000, 2001, 2008 Bernie Innocenti <bernie@codewiz.org>
+ * Copyright 2008 Bernie Innocenti <bernie@codewiz.org>
  * -->
  *
- * \brief Simple realtime multitasking scheduler.
- *        Context switching is only done cooperatively.
+ * \brief Simple preemptive multitasking scheduler.
  *
- * \version $Id: proc.c 1616 2008-08-10 19:41:26Z bernie $
+ * All voluntary and preemptive context switching happens on exit from
+ * a common interrupt (signal) dispatcher.  Preemption on quantum timeout
+ * is regulated by a soft-timer.  Other kinds of preemption could happen
+ * if an interrupt sends a signal to a higher priority process (but this
+ * is still unimplemented).
+ *
+ * In the POSIX implementaiton, context switching is done by the portable
+ * SVR4 swapcontext() facility.
+ *
+ * \version $Id$
  * \author Bernie Innocenti <bernie@codewiz.org>
- * \author Stefano Fedrigo <aleph@develer.com>
  */
 
+#include "cfg/cfg_proc.h"
+
+#if CONFIG_KERN_PREEMPT
+
 #include "proc_p.h"
 #include "proc.h"
+#include "idle.h"
 
+#include <kern/irq.h>
+#include <kern/monitor.h>
+#include <cpu/frame.h> // CPU_IDLE
+#include <cpu/irq.h>   // IRQ_DISABLE()...
+#include <drv/timer.h>
+#include <cfg/module.h>
+#include <cfg/depend.h>    // CONFIG_DEPEND()
 
-/*
- * The time sharing scheduler forces a task switch when the current
- * process has exhausted its quantum.
- */
-uint16_t Quantum;
+// Check config dependencies
+CONFIG_DEPEND(CONFIG_KERN_PREEMPT, CONFIG_KERN && CONFIG_TIMER_EVENTS && CONFIG_KERN_IRQ);
 
-/**
- * Disable preemptive task switching.
- *
- * The scheduler maintains a per-process nesting counter.  Task switching is
- * effectively re-enabled only when the number of calls to proc_permit()
- * matches the number of calls to proc_forbid().
- *
- * Calling functions that could sleep while task switching is disabled
- * is dangerous, although supported.  Preemptive task switching is
- * resumed while the process is sleeping and disabled again as soon as
- * it wakes up again.
- *
- * \sa proc_permit()
- */
-void proc_forbid(void)
+MOD_DEFINE(preempt)
+
+/// Global preemption disabling nesting counter
+cpu_atomic_t _preempt_forbid_cnt;
+
+static Timer preempt_timer;
+
+
+void proc_schedule(void)
 {
-       /* No need to protect against interrupts here. */
-       ++CurrentProcess->forbid_cnt;
+       IRQ_DISABLE;
+
+       ASSERT(proc_preemptAllowed());
+       LIST_ASSERT_VALID(&ProcReadyList);
+       CurrentProcess = (struct Process *)list_remHead(&ProcReadyList);
+       ASSERT2(CurrentProcess, "no idle proc?");
+
+       IRQ_ENABLE;
+
+       TRACEMSG("launching %p:%s", CurrentProcess, proc_currentName());
 }
 
-/**
- * Re-enable preemptive task switching.
- *
- * \sa proc_forbid()
- */
-void proc_permit(void)
+void proc_preempt(UNUSED_ARG(void *, param))
+{
+       if (proc_preemptAllowed())
+       {
+               IRQ_DISABLE;
+
+               #if CONFIG_KERN_PRI
+                       Process *rival = (Process *)LIST_HEAD(&ProcReadyList);
+                       if (rival && rival->link.pri >= CurrentProcess->link.pri)
+                       {
+               #endif
+
+               TRACEMSG("preempting %p:%s", CurrentProcess, proc_currentName());
+
+// FIXME: this still breaks havoc, probably because of some reentrancy issue
+#if 0
+               SCHED_ENQUEUE(CurrentProcess);
+               proc_schedule();
+#endif
+               #if CONFIG_KERN_PRI
+                       }
+               #endif
+
+               IRQ_ENABLE;
+       }
+
+       timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
+       timer_add(&preempt_timer);
+}
+
+void proc_switch(void)
+{
+       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+       TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
+       ATOMIC(LIST_ASSERT_VALID(&ProcReadyList));
+
+       /* Sleeping with IRQs disabled or preemption forbidden is illegal */
+       IRQ_ASSERT_ENABLED();
+       ASSERT(proc_preemptAllowed());
+
+       // Will invoke proc_switch() in interrupt context
+       kill(0, SIGUSR1);
+}
+
+void proc_yield(void)
 {
-       /* No need to protect against interrupts here. */
-       --CurrentProcess->forbid_cnt;
+       TRACEMSG("%p:%s", CurrentProcess, proc_currentName());
+
+       IRQ_DISABLE;
+       SCHED_ENQUEUE(CurrentProcess);
+       IRQ_ENABLE;
+
+       proc_switch();
 }
+
+void proc_entry(void (*user_entry)(void))
+{
+       user_entry();
+       proc_exit();
+}
+
+void preempt_init(void)
+{
+       MOD_CHECK(irq);
+       MOD_CHECK(timer);
+
+       irq_register(SIGUSR1, proc_schedule);
+
+       timer_setSoftint(&preempt_timer, proc_preempt, NULL);
+       timer_setDelay(&preempt_timer, CONFIG_KERN_QUANTUM);
+       timer_add(&preempt_timer);
+
+       idle_init();
+
+       MOD_INIT(preempt);
+}
+
+#endif // CONFIG_KERN_PREEMPT